CN111180473A - CMOS image sensor pixel structure with high charge transfer efficiency - Google Patents
CMOS image sensor pixel structure with high charge transfer efficiency Download PDFInfo
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- CN111180473A CN111180473A CN201811328811.9A CN201811328811A CN111180473A CN 111180473 A CN111180473 A CN 111180473A CN 201811328811 A CN201811328811 A CN 201811328811A CN 111180473 A CN111180473 A CN 111180473A
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- 238000009792 diffusion process Methods 0.000 claims abstract description 22
- 230000005684 electric field Effects 0.000 claims abstract description 6
- 230000005540 biological transmission Effects 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 4
- 238000010351 charge transfer process Methods 0.000 claims description 3
- 230000033001 locomotion Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000005036 potential barrier Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
- H01L27/1461—Pixel-elements with integrated switching, control, storage or amplification elements characterised by the photosensitive area
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Abstract
A double-ring pixel structure increases a transfer channel of photo-generated charges from a photodiode to a floating diffusion node, increases an electric field on a charge transfer path, shortens the diffusion distance of the charges in a flat potential region, and can effectively improve the transfer speed and efficiency of the charges, thereby completing the rapid and complete transfer of the charges and improving the performance of a large-pixel CMOS image sensor.
Description
Technical Field
The invention belongs to the field of CMOS image sensors, and particularly relates to a CMOS image sensor pixel structure with high charge transfer efficiency.
Background
PPD was originally used in CCD image sensors and was not used in CMOS image sensors for more than twenty years. Fig. 1 is a PPD-based 4T pixel structure. The 4T pixel is composed of a clamping photodiode (PPD), a transmission tube, a reset tube, a row gate tube and a floating diffusion node. The charge transfer case is one of the very important performance parameters for a PPD image sensor. Ideally, all of the photo-generated electrons integrated in the PPD region are transferred and read out.
In the pixel part of the image sensor, after the exposure integration is completed, the transmission tube can control photo-generated charges to be transferred from the photodiode region to the floating diffusion node region, and whether the complete transfer of the charges can be realized depends on whether a potential barrier or a potential well exists on a charge transfer path and the charge capacity of the floating diffusion node under the condition that the transmission tube is conducted. There are two types of motion for the transfer of charge: drift motion under the influence of an electric field and diffusion motion. The transfer rate of photo-generated charge depends primarily on the length of the transfer path and the distance of diffusion movement in the "flat potential" region.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a CMOS image sensor pixel structure with high charge transfer efficiency, which adopts an annular layout structure, and reads out signal voltage by arranging a photodiode at the middle position, arranging transmission tubes and floating diffusion nodes at two sides, and connecting the floating diffusion nodes at the two sides through metal wires; the structure can shorten the diffusion distance of photo-generated charges, increase the electric field on a transfer path and improve the transfer speed of the photo-generated charges, thereby realizing the quick and complete transfer of the charges, eliminating the tailing phenomenon and improving the performance of the CMOS image sensor.
A CMOS image sensor pixel structure with high charge transfer efficiency, such as the double annular large photo-sensitive area pixel layout of FIG. 2. After exposure is finished, the photodiode finishes a photoelectric conversion process, photo-generated charges are stored in a photodiode region, transmission tubes on two sides are opened simultaneously, and the photo-generated charges are transferred to a floating diffusion node region from the photodiode, which is different from a traditional pixel structure consisting of a rectangular PPD, the transmission tubes and the floating diffusion nodes shown in figure 3. After the photo-generated electrons are transferred to the floating diffusion node to complete the charge-voltage conversion process, the signal voltage is read out through the source follower and the selection tube.
A double-ring pixel structure increases a transfer channel of photo-generated charges from a photodiode to a floating diffusion node, increases an electric field on a charge transfer path, shortens the diffusion distance of the charges in a flat potential region, and can effectively improve the transfer speed and efficiency of the charges, thereby completing the rapid and complete transfer of the charges and improving the performance of a large-pixel CMOS image sensor.
Drawings
FIG. 1 is a basic structure diagram of a 4T pixel;
FIG. 2 is a cross-sectional view of a dual ring pixel structure;
fig. 3 is a cross-sectional view of a conventional pixel structure.
Detailed Description
A CMOS image sensor pixel structure with high charge transfer efficiency is characterized in that a double-ring layout structure is introduced, transmission tubes and floating diffusion nodes exist in the periphery of a photodiode region, the channel for transferring photo-generated charges from the photodiode to the floating diffusion nodes is equivalently widened, the distance of a flat potential region is shortened, namely in the charge transfer process, the charges do not need to be transferred only to the same direction, and a better transfer path with a larger electric field can be selected by the CMOS image sensor pixel structure.
The CMOS image sensor pixel structure with high charge transfer efficiency is suitable for pixels with large photosensitive areas, can ensure high full-well capacity, improve charge transfer speed, realize complete charge transfer and eliminate image tailing. For example, PPD of 8um × 8um has a full well capacity as high as twenty thousand, and if the conventional pixel unit structure of fig. 3 is adopted, a large amount of charges remain in the PPD region, which causes image smearing; the double-ring structure provided by the invention can provide more transfer channels and charge storage capacity, and in the charge transfer process, photo-generated charges can be transferred by selecting a path with smaller resistance and can respectively enter two floating diffusion nodes, so that the effective full-well capacity of pixels is increased, the trailing phenomenon is eliminated, and the signal-to-noise ratio of the image sensor is improved.
By adopting the process parameters, structural optimization based on a PPD structure can be realized, and the pixel unit design with high charge transfer efficiency can be realized on the basis of ensuring a large photosensitive area and full-well capacity.
Claims (1)
1. A CMOS image sensor pixel structure with high charge transfer efficiency, characterized by: adopting a double-ring large-photosensitive-area pixel layout; after exposure is finished, the photodiode finishes a photoelectric conversion process, photo-generated charges are stored in a photodiode region, transmission tubes on two sides are opened simultaneously, and the photo-generated charges are transferred to a floating diffusion node region through the photodiode; the transmission tubes and the floating diffusion nodes are arranged on the periphery of the PPD region, so that the channel for transferring photo-generated charges from the photodiode to the floating diffusion nodes can be equivalently widened, the distance of a flat potential region is shortened, namely, in the charge transfer process, the charges can be transferred in the same direction, and a better transfer path with a larger electric field can be automatically selected; after the photo-generated electrons are transferred to the floating diffusion node to complete the charge-voltage conversion process, the signal voltage is read out through the source follower and the selection tube.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201811328811.9A CN111180473A (en) | 2018-11-09 | 2018-11-09 | CMOS image sensor pixel structure with high charge transfer efficiency |
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| CN201811328811.9A CN111180473A (en) | 2018-11-09 | 2018-11-09 | CMOS image sensor pixel structure with high charge transfer efficiency |
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| CN111180473A true CN111180473A (en) | 2020-05-19 |
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| CN201811328811.9A Pending CN111180473A (en) | 2018-11-09 | 2018-11-09 | CMOS image sensor pixel structure with high charge transfer efficiency |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112614862A (en) * | 2020-12-29 | 2021-04-06 | 长春长光辰芯光电技术有限公司 | Novel CMOS image sensor pixel structure |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20120112255A1 (en) * | 2009-07-10 | 2012-05-10 | Tohoku University | Solid-State Image Sensor |
| CN104134676A (en) * | 2014-07-23 | 2014-11-05 | 中国航天科技集团公司第九研究院第七七一研究所 | Rapid charge transfer pixel structure based on radiation environment application |
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2018
- 2018-11-09 CN CN201811328811.9A patent/CN111180473A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20120112255A1 (en) * | 2009-07-10 | 2012-05-10 | Tohoku University | Solid-State Image Sensor |
| CN104134676A (en) * | 2014-07-23 | 2014-11-05 | 中国航天科技集团公司第九研究院第七七一研究所 | Rapid charge transfer pixel structure based on radiation environment application |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112614862A (en) * | 2020-12-29 | 2021-04-06 | 长春长光辰芯光电技术有限公司 | Novel CMOS image sensor pixel structure |
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Application publication date: 20200519 |
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